AP Macroeconomics common mistakes
AP Macroeconomics · Understand the traps and how to avoid them.
Labeling a supply-and-demand graph shift by moving the curve but forgetting to show the new equilibrium price and quantity, or drawing the shift without an arrow indicating direction.
Candidates focus on the curve movement itself and treat the equilibrium intersection as implicit, so they never mark P2 and Q2 or the arrow.
What to do instead
Adopt a fixed drawing routine: shift the curve, draw an arrow from old to new curve, then mark the new intersection with dashed lines to both axes and label P1, P2, Q1, Q2.
Treating a change in the price of the good as a shift of the demand or supply curve rather than a movement along the curve.
The words 'price changes' trigger a reflexive 'curve moves' response because students memorize 'demand changes = curve shifts' without distinguishing determinants from price.
What to do instead
Before drawing, list the non-price determinants of demand (income, tastes, related-good prices, expectations, number of buyers) and check whether the change is on that list; if the change is the good's own price, move the point along the existing curve.
Confusing a change in the price level (which moves along the aggregate demand curve) with a change in a spending component such as government spending (which shifts aggregate demand).
The AD curve looks like a normal demand curve, so students apply micro logic and shift it for price-level changes or fail to shift it for fiscal policy.
What to do instead
Memorize the three reasons AD slopes down (wealth, interest-rate, exchange-rate effects) as price-level effects only, and practice sorting a list of shocks into 'move along AD' versus 'shift AD' before graphing.
Omitting the money-market or loanable-funds transmission step when explaining how a central bank policy change affects output and the price level.
Candidates jump from 'the Fed buys bonds' straight to 'GDP rises,' skipping the interest rate, investment, and aggregate demand links that earn explanation points.
What to do instead
Write the chain explicitly every time: policy tool → reserves/money supply → nominal interest rate → investment and consumption → aggregate demand → real GDP and price level, and check each arrow is present.
Mixing up which curve shifts for a supply shock versus a demand shock on the AS/AD model, for example shifting AD for an oil price increase.
Input-cost events feel like they should affect demand because they raise prices, and students do not firmly attach input prices to the short-run aggregate supply curve.
What to do instead
Build a two-column sort: determinants of SRAS (input prices, productivity, taxes/subsidies on firms, expected inflation) versus determinants of AD; classify each practice shock before graphing.
Calculating the spending multiplier as 1/(1+MPC) or forgetting that the multiplier applies to the initial change in spending, not to the full new spending level.
Formula memorization without understanding that the multiplier comes from an infinite geometric series with ratio MPC.
What to do instead
Derive the multiplier once from the series 1 + MPC + MPC^2 + ..., confirm it equals 1/(1−MPC), and always compute total change in GDP as (initial change in autonomous spending) × multiplier.
Reporting a nominal GDP increase as real growth without adjusting for the price index, or deflating in the wrong direction.
Students see a larger dollar figure and assume growth, and they misremember whether to divide or multiply by the price index.
What to do instead
Use real GDP = nominal GDP / (price index/100) and sanity-check: if the price level rose faster than nominal GDP, real GDP must have fallen; state the direction in words before computing.
Classifying a person as unemployed or out of the labor force incorrectly, for example counting discouraged workers as unemployed or excluding part-time workers from employment.
The official definitions are narrow and counterintuitive; students apply everyday intuition instead of the BLS criteria.
What to do instead
Apply a decision tree: worked at least one hour for pay in the reference week → employed; did not work but actively searched and available → unemployed; otherwise → not in labor force; then compute the unemployment rate as unemployed/labor force.
Describing a policy as expansionary or contractionary based on the size of a budget deficit rather than on the direction of the change in spending or taxes relative to potential output.
Students equate 'deficit' with 'expansionary' and 'surplus' with 'contractionary,' ignoring the structural versus cyclical distinction.
What to do instead
Judge policy by the intended direction of aggregate demand: raising government spending or cutting taxes is expansionary; then separately note that automatic stabilizers change the deficit without a discretionary policy change.
On a foreign exchange graph, shifting the wrong currency's market or reversing appreciation and depreciation when the exchange rate is quoted as a price of foreign currency.
There are two markets (each currency) and two quoting conventions, and students do not anchor to which currency is the 'price' and which is the 'good.'
What to do instead
Write the axis labels as 'price of one euro in dollars' before shifting; then an increase in demand for euros raises the dollar price of a euro, which is euro appreciation and dollar depreciation, and state both sides explicitly.